I'd say to avoid going out with both your partner and their other partner (other significant other, OSO), your metamour. That way you won't have to see them doing "public displays of affection" (PDAs).

I understand it's hard to get used to your formerly monogamous partner being intimate with another. Even just knowing they are is weird, or can be upsetting. But actually seeing it? You don't have to. You can do "parallel polyamory," where two people in a V date the same person, but those two people don't hang out in the same space.

That might be a better idea than trying to do threesome dates, at least for now. You partner can do what they want with others, and you don't have to see it, or hear about it.

I'm sorry you're no longer kissing passionately despite still loving each other. What happened? Is there no sex at all? You want it, but your partner doesn't? Are you sure your partner is really poly, and not just "monkey branching" into a new relationship, prior to leaving you?

I think we need more details. You can vent here. Don't worry about being brief. The more we know, the better feedback we can give.

You may have created a rule and not a boundary, if you expressed it in a way that asked your partner to change their behavior. It doesn't sound like you did, but it does sound like they took it that way. Or maybe you did expect them to make sure not to kiss passionately in front of you?

To clarify:
A boundary is a standard or a framework that you create to protect or support yourself in some way. You are the only person responsible for defending your boundaries.

A rule is an order, guideline, or decree that you place on someone else and expect them to follow.

If it bothers you to see your partner and metamour making out, then you create a boundary for yourself that would be something like, "I will not put myself in social situations where I might see them kiss." And then you remove yourself from a situation where that is occurring, or avoid one where it could occur.

However, that being said, it would seem to me that the polite, respectful thing for them to do would be to consider your feelings and hold back from sucking face in front of you, especially at this early stage of being in a poly arrangement. When I first started learning about polyamory, there was a lot of advice to couples who transitioned from mono to poly to take things slowly and "go at the speed of the one who struggles the most." However, it is still their choice as to whether they will be sensitive to your feelings or not. At some point, you might have to decide whether you will continue in this situation or not. The thing to ask yourself is whether or not you feel valued, respected, and considered by your partner. And if you don't, then what will you do about it?

I wonder if you willingly agreed to poly or felt pressured to do so. I hope you two are checking in with each other periodically to see how you're doing with this big change in your life. If not, when you find a quiet moment, you might express to your partner how uncomfortable you are when seeing them do certain things, but do not blame them for your discomfort nor expect them to change. It's up to you to take care of yourself.

Hello VLD,

It seems reasonable to me to ask your partner not to French/passionately kiss their other partner in front of you. However, it is their choice as to whether to honor your request. You may have to set that as a boundary within yourself, in other words you need to decide how you will respond the next time you see them kissing like that. Maybe you will leave the room. Maybe you will distance yourself from your partner for a period of time. Maybe you will break up with your partner. It's up to you. That's how a boundary works. You decide what you are not okay with, and you decide how you will respond if/when that happens.

Sympathetically,
Kevin T.

Again, the OP doesn't have to distance themselves from their partner, or break up. They can just not go on threesome dates! Simple. Lots of people prefer parallel poly. If you are going to do "garden party poly," where the metamours agree to be in the same space for a special occasion, like for a holiday dinner or the shared partner's birthday, that could happen eventually, once things have gone from, "This is new and different and I am still getting used to it," to, "This is the new normal and it feels okay."

Open and honest communication. Using "I statements." No one giving each other permission, or withholding permission. Just going over what one's own needs are, and figuring out how to get one's needs met. If the poly partner is neglecting the original partner's needs or desires, it could be "NRE (new relationship energy, or infatuation/obsession with the new person) causing poly hell." Here's some reading on that.

Or it could just be the original relationship has run its course, and the "polyamory" is just a way to initiate a breakup. Which is not very kind. And isn't polyamory. Polyamory means loving more than one. It doesn't mean getting all carried away with the new person and stopping acting in loving ways to the established partner.

I get feeling envious that way.

As others have said, it's not a boundary. You can make it a request your partner could say yes or no to... it's always ok to make a request. Trouble is, in this case there's two people involved, so you'd also have to request it from the metamour. (Depending on your relationship, you could try that... I doubt it lands well, but some people may be understanding and save passion for the private.)
If your partner sais no to both your requests... to kiss you as passionately or to refrain from displays of passion with meta when you're around... I say don't go out with them. You can do more parallel poly. (Or just let this guy go, if he can't be considerate, that's ok too.)